OpenEnergyMonitor Community

What do I need for an electricty monitor?

I am slightly confused about how to get my initial setup working.

To monitor my electric supply (via a meter sensor and clip on sensor) what hardware do I need?

Obviously I need the Pi, and sensors. But what else?

Welcome, George, to the OEM forum.

With the amount of information here, that’s hardly surprising. Feel free to ask as much as you like.

A question: Why do you want both the optical pulse detector on your meter, and the current transformer on the cable?
The differences:

  1. The c.t. will give you an “up-to-the (5) second” reading of power, both consumed and, if you have your own generation with PV or something else, exported power too. (That’s because it reads the current and calculates power every 5 s.)
  2. The pulse sensor will only read imported energy, and only when 1 pulse’s worth (see the front of the meter to know what that is) has been consumed. If you have generation, the meter won’t normally pulse when exporting.
  3. The c.t. will not be as accurate as the meter (which by definition is 100% accurate) due to calibration errors, which might still be present even if you have test lab. instruments to calibrate against.

You can of course have both: you might want to calibrate the c.t. against your meter to give long-term accuracy to its readings.

If you get an emonPi, then in addition to the optical pulse sensor and/or the c.t., you’ll need a 5 V d.c. USB power supply and lead, and if you have the c.t., you’ll probably want an a.c. adapter too to measure the voltage and hence give you an accurate value for power and energy. (Without the a.c. adapter, it can’t tell the difference between imported and exported power, and it assumes a 230 V supply always, which is wrong on two counts: the UK mains is still centred on 240 V, and it’s rarely exactly 240 V anyway.)

You’ll also need to be within WiFi range of your router, or have a wired Ethernet connection to your router.

That should be all you need to get going.

Thank you. Point taken about the sensor, will use the optical one.

So, can I reuse my existing Raspberry Pi?

The emonPi product looks like a complete package and includes the Pi, a secondary board and the rather neat aluminum case.



If you’re only ever going to be using the pulse sensor, then unless you can persuade the shop to sell you a case, you’ll need either the emonPi p.c.b. (which gives you the analogue front end which you don’t want, in addition to the pulse input which you do); or you’ll need to connect the optical pulse sensor to the GPIO of your RPi and write a service or a Python script to count pulses, calibrate the count in kWh and send that value into emonCMS. Here’s how to do that: Directly connecting to Optical Pulse Counter with RPi?
(And you’ll need to download and set up emonCMS on your RPi).

The aluminium enclosure is available separately in the shop:

I looked for that under the emonPi options, couldn’t see it, so presumed it was no longer available separately.

Do you have the link for the emonPi analogue PCB? I can’t find it!

Are you looking to purchase?

“PCB Only” option here:

or do you want technical information, which is here:

I didn’t mention the pcb because it seems a very expensive way to get the pulse input, which is all the ‘emon’ board will give you.